Portable or mobile devices originally introduced as mobile phones or electronic agendas become more and more ubiquitous. As the processing power of their internal processors grows and equally the bandwidth for communication with remote or stationary processors, such portable devices take on more and more the role of multi-purpose tools available to consumers and specialist users alike.
It has been recognized that portable devices can benefit from the presence of sensors capable of providing a chemical analysis of materials brought into contact or the vicinity of the device. Whilst there are many possible applications for such sensors, it suffices to consider for example the analysis of air surrounding the portable device. Such an analysis can be useful for multiple purposes such as testing for hazardous gases, breath analysis for general medical purposes or driving fitness, and the like.
Specialized portable devices for testing the breath for alcohol are well known and widely used by law enforcing authorities as preliminary test kits for blood alcohol concentration (BAC). One conventional method to measure BAC of a person requires the person to fully exhale into a mouthpiece coupled to an apparatus that uses a fuel cell sensor to measure the ethanol vapor concentration in the exhaled breath emerging near the end of the exhalation.
However, some people find this unpleasant and generally a mouthpiece is not acceptable in mobile devices of the present invention, which are typically designed to have multiple purposes not necessarily restricted to solely breath analysis. Other conventional methods and apparatus for measuring BAC do not require a person to exhale into a mouthpiece, but rely generally on a valve to route a second source of air without exhaled breath or without ethanol gas to serve as a baseline for determining ethanol gas concentration. Other methods rely on complicated signal analysis techniques that compare waveforms from an ethanol gas detector and a carbon dioxide gas detector.
It has been proposed to equip vehicles with blood alcohol concentration (BAC) sensors to estimate the BAC of a person attempting to operate a vehicle based on the concentration of ethanol gas in the breath of the person. Such attempts are described for example in the U.S. Pat. Nos. 5,531,225 A, 8,183,527 B, the published United States patent application US 2010/0188232 and other documents. These devices are typically designed for the specific purpose of analyzing the breath for alcohol content and form a permanent fixture of the car they are installed in.
It has further been recognized that devices which receive a mixture of breath and surrounding air require compensation for the dilution caused by the surrounding air. As described in the above cited documents, the compensation can be done using for example—in parallel to such devices—humidity measurements, other chemical measurements (e.g. CO2, O2 concentrations) or temperature measurements.
Humidity sensors for mobile applications are described for example in the published United States patent application US 2012/231841 and ways of manufacturing miniaturized sensors as MEMS devices with CMOS connections and circuitry are described for example in the published international patent application WO 2012/100362 A1. Metal-oxide sensors with integrated heaters are described for example in the international patent application WO 95/19563.
For general purpose portable devices the problem of making an accurate measurement and compensating for example for the effects of dilution becomes compounded by the dimension of the opening or openings through which the sensor receives the sample of exhaled air. It is therefore seen as an object of the present invention to improve the accuracy of the measurement of alcohol concentration or other components in a sample of exhaled breath using a multi-purpose portable electronic device.